any comments on the difficulty of a single tier system with two pumps to sparge and pump to boil kettle? Is it impossible or just a game of controlling in/out on both pumps? Is a stuck mash a given or can it be done routinely? thanks, doc

Stuck sparges depend more on the false bottom and/or manifold in your HLT. Single tier can also be done easily with a single pump if you're not trying to recirculate during the mash - just put quick-disconnects on your kettles and swap hoses around as needed.

I guess my big question is if the out of mash tun is same height as in of boil kettle then if let passive flow from mash go into boil wouldnt eventually the flow stop? maybe stupid physics question but still dont get it

If you want to fly sparge (slowly sprinkle strike water over the top of the grain bed while slowly draining wort to the boil kettle at the same rate), you'll need either two pumps or a height difference. Height difference isn't too hard to come by though - can transfer the heated water to a cooler and place that on a stand, or can drain the wort to a smaller container below the MLT and carefully pour into the boil kettle when full.

If you batch sparge (add strike water to mash, stir like mad, then drain wort), then you don't need either. Connect pump inlet to HLT to transfer strike water to MLT, get your forearm workout, connect pump inlet to MLT to transfer wort to boil kettle. That's how I've got it set up for single pump, single tier.